Conventionally, iron powder-containing dust generated at the time of converter blowing is wet-collected, then separated by a coarse particle separator into, for example, iron powder-containing dust having a particle diameter of 60 μm or more and iron powder-containing dust having a particle diameter of less than 60 μm, and collected. The iron powder-containing dust having a particle diameter of less than 60 μm is formed into briquette and reused as a cooling agent or an iron source in the converter process. Specifically, the briquette of the iron powder-containing dust is charged into a converter furnace together with molten iron which is produced in a blast furnace and subjected to a pretreatment processing such as desulfurization and dephosphorization, as needed. The molten iron is decarburized to produce molten steel. The molten steel is solidified in continuous casting equipment and then subjected to a processing such as rolling or forging to produce a steel material. In the converter process, from the standpoint of obtaining a function as a cooling agent and preventing spontaneous combustion during stock of the briquette, the metallic iron content of iron powder-containing dust forming the briquette is regulated to 10 mass % or less. Therefore, there is a problem that despite iron powder-containing dust originally having a high metallic iron content, the dust recycled to the converter process is not effectively utilized as a metallic iron resource.
To solve this problem, Patent Document 1 discloses a method for recycling processing of dust generated in a converter furnace, where a low cost and a short processing time are realized and the yield in the converter process can be increased by recycling iron powder-containing dust as metallic iron to a converter furnace. In this recycling processing method, the minimum particle diameter (separation particle diameter) of iron powder-containing dust removed by a coarse particle separator is, for example, 60 μm, and a cake having a size of length of 1,200 mm, width of 1,200 mm and thickness of about 30 mm is produced using the remaining iron powder-containing dust (less than 60 μm), dried to reduce the water content of the cake to 10% or less, and temporarily stored at a scrap yard provided in the vicinity of a converter shop, where according to the converter operation, the cake during storage is charged into a high-temperature converter through a scarp shoot. Here, when a cake containing water component is charged into a converter furnace, the water component in the cake evaporates in a short time and if the water content of the cake is high, the cake undergoes steam explosion, as a result, the cake cannot be charged into a converter furnace. However, when the water content of the cake is 10% or less, the cake can be charged into a converter furnace. On the other hand, the iron powder-containing dust of 60 μm or more removed by a coarse particle separator is dried and thereafter, directly charged into a converter furnace by using a scrap shoot.